As global green and low-carbon challenges intensify,?sustainable radical innovation (SRI)?in these sectors has become crucial for business survival. However, first-mover firms face a unique?“legitimacy-differentiation” paradox—a disruptor’s dilemma—when pursuing radical innovation, unlike their latecomer counterparts. Drawing upon?optimal distinctiveness theory?and?liminal movement theory, this study constructs a process model detailing how first-movers cope with this dilemma. Our findings reveal three core mechanisms. First, first-mover firms sequentially adopt legitimacy strategies of creating external linkages, augmenting green meaning, and leveraging in-depth co-creation, exhibiting a progressively escalating logic from initiation , transmission to collaboration. They also employ differentiation strategies of anchoring value direction, extending value chains, and designing value spaces, demonstrating a leaping logic from point, line to surface. Second, as this asymmetric process unfolds, first-movers achieve?optimal distinctiveness?through a?liminal movement?characterized by contextualized deployment, leadership projection, and dynamic adjustment between legitimacy and differentiation needs. Third, the iterative achievement of optimal distinctiveness enables firms to realize sequential?“front-to-back” technology integration?and?“top-down” technology deepening?within green and low-carbon core technologies. This paper contributes to the literature on radical innovation by first-movers in core technology within the Chinese context and refines the internal mechanisms of optimal distinctiveness through the lens of liminal movement.